gtp: put back reference to netns when not required anymore

This patch fixes a netns leak.

Fixes: 93edb8c7 ("gtp: reload GTPv1 header after pskb_may_pull()")
Reported-by: NCong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: NPablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/gtp.c

@@ -1028,8 +1028,11 @@ static int gtp_genl_new_pdp(struct sk_buff *skb, struct genl_info *info)
 
 	/* Check if there's an existing gtpX device to configure */
 	dev = gtp_find_dev(net, nla_get_u32(info->attrs[GTPA_LINK]));
-	if (dev == NULL)
+	if (dev == NULL) {
+		put_net(net);
 		return -ENODEV;
+	}
+	put_net(net);
 
 	return ipv4_pdp_add(dev, info);
 }
@@ -1051,8 +1054,11 @@ static int gtp_genl_del_pdp(struct sk_buff *skb, struct genl_info *info)
 
 	/* Check if there's an existing gtpX device to configure */
 	dev = gtp_find_dev(net, nla_get_u32(info->attrs[GTPA_LINK]));
-	if (dev == NULL)
+	if (dev == NULL) {
+		put_net(net);
 		return -ENODEV;
+	}
+	put_net(net);
 
 	gtp = netdev_priv(dev);
 
@@ -1163,8 +1169,11 @@ static int gtp_genl_get_pdp(struct sk_buff *skb, struct genl_info *info)
 
 	/* Check if there's an existing gtpX device to configure */
 	dev = gtp_find_dev(net, nla_get_u32(info->attrs[GTPA_LINK]));
-	if (dev == NULL)
+	if (dev == NULL) {
+		put_net(net);
 		return -ENODEV;
+	}
+	put_net(net);
 
 	gtp = netdev_priv(dev);